1. Field of the Invention
The present invention relates to an electronic component packaging structure provided with a moisture-proof coating. In particularly, the present invention relates to an electronic component packaging structure that is covered on the surface thereof by a moisture-proof coating layer protecting the electronic components after completion, while the moisture-proof coating layer can be easily peeled off during repairing.
2. Description of the Related Art
In recent years, there has been a trend toward the use of expensive electronic components on circuit boards used in electric systems of automobiles and aircraft, as electronic apparatuses are required to have increasingly higher performance, higher functions and higher degree of integration. Moreover, the electric systems are required to have high reliability and high durability against harsh operating environment including high temperature, high humidity, watering, dust and vibration. To meet such requirements, such circuit boards provided with moisture-proof coating are used as electronic components including semiconductor devices are covered by a coating material (refer to Japanese Patent Publications JP07-173435A and JP2001-168501A).
On such circuit boards, too, very expensive electronic components have come to be used in large quantities, in an attempt to achieve higher performance, higher functions and higher degree of integration. In case a defect is found in part of the circuit board after mounting the electronic components on the circuit board, repairing operation is often carried out by removing the defective electronic component from the circuit board and reusing functional electronic components.
To repair an electronic component packaging structure that is covered on the surface by a moisture-proof coating layer, it is necessary to peel off the moisture-proof coating layer from the electronic component packaging structure or dissolve the moisture-proof coating layer with an appropriate solvent, then heat the circuit board partially to the solder melting temperature and remove the electronic component. For the moisture-proof coating layer, polymer materials such as acrylic resin and silicone resin (refer to Japanese Patent Publication JP2000-327921A) are commonly used. When repairing, such a polymer material is removed by peeling off the polymer material sheet while heating, dissolving the polymer material with an organic solvent that can dissolve the polymer material, or peeling off the polymer material that has been caused to swell somewhat by putting it into contact an organic solvent that can cause the polymer material to swell.
When repairing an electronic component packaging structure where a polymer material of silicone resin is used as the moisture-proof coating layer, it is a common practice to cause the moisture-proof coating layer to swell by means of an organic solvent such as alcohol or ketone, then peel off the moisture-proof coating layer from the circuit board. In this case, the polymer material of silicone resin tends to rupture along the surface as it is unable to maintain the form of layer or sheet that extends over the surface of the circuit board. As a result, the polymer material of the moisture-proof coating layer remains stuck onto the circuit board in the form of relatively small pieces of scraps. To remove the polymer material of the moisture-proof coating layer remaining in such a form from the circuit board, it has been required to manually peel off each piece by means of a tool such as tweezers. It takes much time and labor to remove the polymer material of the moisture-proof coating layer completely from the circuit board by such a manual operation.